Forming electroplated inductor structures for integrated circuits

ABSTRACT

Methods and associated structures of forming microelectronic devices are described. Those methods may include forming a magnetic material on a substrate, wherein the magnetic material comprises rhenium, cobalt, iron and phosphorus, and annealing the magnetic material at a temperature below about 330 degrees Celsius, wherein the coercivity of the annealed magnetic material is below about 1 Oersted.

BACKGROUND OF THE INVENTION

Magnetic materials may be used to fabricate microelectronic devices,such as inductor and transformer devices. Inductors and transformerstructures may be used in microelectronic circuits such as voltageconverters, on-chip and on-package voltage converters, RF high-frequencycircuits, radar applications and EMI noise reduction circuits. To obtainthe maximum inductance when operating at high frequencies, for example,magnetic flux loss should be minimized.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming that which is regarded as the present invention,the advantages of this invention can be more readily ascertained fromthe following description of the invention when read in conjunction withthe accompanying drawings in which:

FIGS. 1 a-1 g represent structures according to embodiments of thepresent invention.

FIGS. 2 a-2 e represent graphs according to embodiments of the presentinvention.

FIG. 3 represents a flow chart according to embodiments of the presentinvention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

In the following detailed description, reference is made to theaccompanying drawings that show, by way of illustration, specificembodiments in which the invention may be practiced. These embodimentsare described in sufficient detail to enable those skilled in the art topractice the invention. It is to be understood that the variousembodiments of the invention, although different, are not necessarilymutually exclusive. For example, a particular feature, structure, orcharacteristic described herein, in connection with one embodiment, maybe implemented within other embodiments without departing from thespirit and scope of the invention. In addition, it is to be understoodthat the location or arrangement of individual elements within eachdisclosed embodiment may be modified without departing from the spiritand scope of the invention. The following detailed description is,therefore, not to be taken in a limiting sense, and the scope of thepresent invention is defined only by the appended claims, appropriatelyinterpreted, along with the full range of equivalents to which theclaims are entitled. In the drawings, like numerals refer to the same orsimilar functionality throughout the several views.

Methods and associated structures of forming a microelectronic structureare described. Those methods may include forming a magnetic material ona substrate, wherein the magnetic material comprises rhenium, cobalt,iron and phosphorus, and annealing the magnetic material at atemperature below about 330 degrees Celsius, wherein the coercivity ofthe annealed magnetic material is below about 1 Oersted. Methods of thepresent invention enable the fabrication of microelectronic devices,such as, for example, inductor and transformer structures that exhibitlow coercivity and can withstand temperatures of up to about 330 degreesCelsius, thus allowing for improved device performance and compatibilitywith complementary metal oxide semiconductor (CMOS) processingtemperatures.

FIGS. 1 a-1 g illustrate an embodiment of a method of forming amicroelectronic structure, such as an inductor structure, for example.FIG. 1 a illustrates a cross-section of a portion of a substrate 100.The substrate 100 may be comprised of materials such as, but not limitedto, silicon, silicon-on-insulator, germanium, indium antimonide, leadtelluride, indium arsenide, indium phosphide, gallium arsenide, galliumantimonide, or combinations thereof.

The substrate 100 may further comprise microelectronic packagingmaterials and structures as are known in the art. In one embodiment, thesubstrate 100 may include transistors and other devices that, together,form a microprocessor. In an embodiment, the substrate 100 may includedevices that together form multiple microprocessor cores on a singledie. In one embodiment, the substrate may include CMOS devicescomprising multi-level metallization.

A first layer of a magnetic material 102 may be formed on the substrate100 (FIG. 1 b). In one embodiment, the magnetic material 102 maycomprise high-frequency amorphous magnetic materials. In one embodiment,the magnetic material 102 may comprise cobalt, rhenium, phosphorus andiron. The first layer of magnetic material 102 may comprise a thickness103 of about 0.1 microns to about 30 microns.

The first layer of magnetic material 102 may be formed utilizingelectro-deposition techniques such as electroplating, pulse reverseelectroplating and/or pulse plating at two or more current densities. Inone embodiment, an electroplating bath that may be used in anelectro-deposition process may comprise a cobalt salt such as cobaltchloride, a source of phosphorous such as phosphorous acid, a source ofrhenium such as potassium perrhenate or sodium perrhenate and othercomponents as required such as phosphoric acid and cobalt carbonate. Inan embodiment, the phosphorous acid may comprise a concentration ofabout 30 grams per liter to about 65 grams per liter, the phosphoricacid may comprise about 50 grams per liter, the cobalt chloride.6H20 maycomprise about 181 grams per liter, the cobalt carbonate may compriseabout 39.4 grams per liter, and the potassium perrhenate may comprise aconcentration of about 0.7 grams per liter. In one embodiment, theelectroplating bath may comprise at least one of CoSO4.6H20 andCoCl2.6H20.

In an embodiment, the electroplating process can be performed by firstpatterning a photoresist material on top of a seed layer (not shown),such as a 20 nm titanium layer followed by a 0.1˜0.2 um thick copperseed layer or a 0.3 um thick cobalt seed layer, for example, and thenfilling the exposed areas with the magnetic material 102. In oneembodiment, a 0.1 micron thick copper seed layer may be formed on aplanar surface, such as the substrate 100. The magnetic material 102 canalso be formed on the substrate 100 by using an electroless platingprocess, wherein boron may be added to the chemistry, therebyeliminating the need for a seed layer.

The electrodeposited magnetic material 102 may exhibit both highresistivity and low coercivity. Consequently the magnetic material 102may comprise both low eddy current loss and low hysteresis loss. In oneembodiment, low coercivity may be achieved by utilizing an approachother than simple direct current (DC) electroplating, since plane DCplated films may exhibit perpendicular anisotropy, and hence very lowpermeability and high values of coercivity, in some cases.

In one embodiment, a magnetic material comprising an in-plane anisotropyand low coercivity may be achieved by forming a multilayer structure ofalternating compositions. This multilayer structure may be created usingeither pulse reverse plating and/or pulse plating at two differentcurrent densities. An example of a pulse reverse waveform is shown inFIG. 2 a, comprising a forward current density (CD) 203, a reverse CD205, a forward time 209, an off time of 2 times 211 and a reverse time207. The particular current densities and pulse times will varyaccording to the particular application. The effect of such a pulsereverse plating process on the formation of a magnetic materialcomprising CoPRe, for example, (such as the magnetic material 102), isshown in FIG. 1 c.

An initial portion 115 of the magnetic material 102 may be formed duringthe forward time 209. A portion 104 of the plated magnetic material maybe removed during the reverse time 207 and that removal may leave behinda phosphorous rich region 106, relative to a low phosphorousconcentration/percentage region 108. This process of forming alternatinghigh phosphorous layers 106 and low phosphorous layers 108 may form amultilayer structure 110 (FIG. 1 e), which may be repeated until adesired total thickness of the magnetic material 102 may be achieved.Alternatively the high and low phosphorous layers can be formed usingpulse plating at two or more current densities. In one embodiment, atotal thickness of the magnetic material 102 may comprise about 0.5microns to about 30 microns. In one embodiment, a first nanolayer ofmaterial may be formed and then a second nanolayer of material may beformed on the first nanolayer of material, wherein one of the firstnanolayer and the second nanolayer comprises a percentage of phosphorusthat is greater than the other of the first nanolayer and the secondnanolayer. The nanolayer with the high phosphorous content may or maynot have a phosphorous content high enough to make the materialnon-magnetic.

Hence a pulse reverse plating process may lead to the formation of amagnetic material 102 that comprises a multilayer structure 110consisting of alternating high phosphorus concentration/percentagelayers and low phosphorous concentration/percentage layers. In oneembodiment, the high percentage phosphorous layer 106 may comprise athickness of below about 5 nm and the low percentage phosphorous layer108 may comprise a thickness of about 40 nm and below. In oneembodiment, the multilayer structure 110 may comprise a multinanolayerstructure 110 and the high and low percentage phosphorous layers 106,108 may comprise high and low percentage phosphorous nanolayers 106,108.

The magnetic material 102, as a ferromagnetic material, can retain amemory of an applied field once the field is removed, which is calledhysteresis. The coercivity is the intensity of the applied magneticfield required to reduce the magnetization of that material back to zeroafter the magnetization has been driven to saturation. For inductors, asmall coercivity is desirable to minimize losses, but is typicallydifficult to achieve. FIGS. 2 b-2 c show the magnetic hysteresis loopsof the magnetic material 102, wherein the magnetic material 102comprises compositions of CoPRe in FIG. 2 a and CoPReFe in FIG. 2 b.

As can be seen, the hard axis (which is the axis that would be used forinductors) 213 a of FIG. 2 b, and the hard axis 213 b of FIG. 2 c forthe CoPRe and CoPReFe compositions respectively is linear and has aminimal coercivity. The coercivity of for these magnetic material 102compositions is about 0.1˜0.3 Oersteds, thereby minimizing magnetichysteretic losses. In addition, the magnetic material 102 has thecapability of withstanding high temperatures, which makes it suitablefor use in CMOS processing. For example, CoP films (for example,Co_(75.8)P_(24.2)), may comprise a coercivity above about 1.4 Oe at roomtemperature and above about 13 Oe after annealing at about 300 degreesCelsius.

By adding rhenium (for example, by forming a magnetic material 102comprising the compositions Co_(78.9)P_(19.9)Re_(1.0) orCo_(79.2)P_(19.4)Re_(1.4)) the coercivity is reduced and the magneticmaterial 102 can withstand high temperatures, such as annealingtemperatures, of up to about 330° C. while maintaining coercivitiesbelow about 0.3 Oersteds. In another embodiment, the magnetic material102 of the present invention may comprise a coercivity of below about 1Oersted, depending upon the particular application. Thus, the magneticmaterial 102 of the present invention is suitable for use in CMOSprocessing, such as in conjunction with the use of polyimides as adielectric material, for example.

Additionally, the iron concentration of the magnetic material 102 can beoptimized to increase the magnetic flux saturation up to about 2.0 Teslain some cases, which is useful for high electric current applications,such as voltage converters. The addition of iron in the magneticmaterial 102 is a further benefit for increasing the resistivity aswell, of the magnetic material 102. In one embodiment, the rheniumconcentrations may comprise about 0.1 to about 5.0 atomic percent of themagnetic material 102. In one embodiment, the coercivity of the magneticmaterial 102 may be optimized by maintaining a phosphorus percentageabove about 14 percent. In another embodiment, the atomic percentage ofphosphorus may comprise about 8 to about 25 percent and the atomicpercentage of rhenium may comprise about 0.1 to about 5 percent. Theparticular concentrations of the rhenium, cobalt, phosphorus and ironmay be varied and optimized depending upon the particular application.

In another embodiment, the phosphorus concentration within the magneticmaterial 102 may be optimized in order to achieve a desired resistivityof the magnetic material 102, which will minimize eddy current dampeningat higher frequencies. FIG. 2 d depicts a graph of the resistivity 215of the magnetic material 102 comprising CoPReFe versus the phosphorusatomic percentage 217. FIG. 2 d shows that the resistivity is about 150μΩ-cm for phosphorus percentages between about 10 to about 16 atomicpercent, (which may be optimized depending upon the composition), whichis about 10 times higher than NiFe permalloy (typically 15-20 mOhm-cm)for example, so that the eddy-current losses may be minimized ascompared with the permalloy. In one embodiment, the resistivity of themagnetic material comprises above about 150 micro-ohm centimeters whenthe phosphorus percentage is above about 14 percent.

The magnetostriction coefficient for the magnetic material 102 maycomprise about 0.5˜1.5×10⁻⁶, significantly lower than pure cobalt at1.0×10⁻⁵. FIG. 2 e shows the permeability 219 versus the frequency 221of electroplated CoPRe magnetic material 102 comprising about 2 micronsin thickness. In some embodiments, the permeability of the magneticmaterial 102 may comprise about 700 at frequencies of up to 150 MHz. Inone embodiment, a resistivity of the magnetic material 102 may comprisebetween about 100 micro ohm-centimeters to about 200 micro-ohmcentimeters, and a permeability of the magnetic material 102 maycomprise about 600 to about 800 from about 0 to about 150 MHz.

Referring back to FIG. 1 e, at least one conductive structure 112 may beformed on a thin dielectric layer 114 disposed between the magneticmaterial 102 and the substrate 100. In one embodiment, the at least oneconductive structure 104 may comprise a copper interconnect structure,such as a copper winding structure for example, that may be used asinductor windings, in some cases, and may comprise a thickness 116 ofabout 1 to about 10 microns. The particular thickness 116 of the atleast one conductive structure 112 will vary according to the particularapplication.

In some embodiments, a dielectric layer 118 such as polyimide layer 118may be formed on and around the at least one conductive structure 112(FIG. 1 f). In one embodiment, the dielectric layer 118 may be formed ona top surface 117 and in the spaces 119 between the individualconductive structures 112.

In one embodiment, a second layer of magnetic material 120 (which maycomprise similar materials to the first layer of magnetic material 102)may be formed on the at least one conductive structure 112 (FIG. 1 g) toform an inductive structure 122. The inductive structure 122 maycomprise various inductor and transformer structures/devices, forexample, and may be used in microelectronic circuits such as on-chipand/or on package voltage converters, RF high-frequency circuits, radarand EMI noise reduction circuits. In one embodiment, the inductivestructure 122 may comprise a portion of a package substrate that maycomprise submicron CMOS devices, and may comprise high-frequencyamorphous magnetic materials and multilevel metallization.

In some devices, to obtain a maximum theoretical increase in inductivemagnetic flux, the two layers of magnetic material 102, 120 need to makecontact so that the magnetic flux loss is minimized to zero. At highoperating frequencies, the apparent inductance of prior art devices maygradually decrease with frequency because there may be losses from eddycurrents that flow in the magnetic material. Thus, carefully designedmagnetic vias serve to maximize the inductance of such high frequencyinductive structures, such as the inductive structure 122.

Without a good magnetic connection, the magnetic flux may escape,resulting in significant loss in inductance for the device. The magneticconnection may comprise a magnetic via 124, which comprises the regionwherein the first layer of magnetic material 102 and the second magneticlayer 120 make contact with each other to complete the circuit for themagnetic flux.

In another embodiment, the magnetic material 102 may comprise a portionof other inductor structures (not shown) that are known in the art. Themagnetic material 102, 120 described herein is not limited for use inthe inductor structure 122, but may find application in any type ofinductor/transformer/microelectronic structure as in known in the art.In addition, the magnetic material 102, 120 may be used inmicroelectronic circuits such as on-chip and/or on package voltageconverters, RF high-frequency circuits, radar and EMI noise reductioncircuits. In one embodiment, the magnetic material 102, 120 may comprisea portion of a package substrate that may comprise submicron CMOSdevices, and may comprise high-frequency amorphous magnetic materialsand multilevel metallization.

In another embodiment shown in FIG. 3, a magnetic material may be formedon a substrate, wherein the magnetic material comprises rhenium, cobalt,and phosphorus at step 302. At step 304, the magnetic material may beannealed at a temperature below about 330 degrees Celsius, wherein thecoercivity of the annealed magnetic material is below about 1 Oersted.In another embodiment, the annealed magnetic material may comprise acoercivity below about 0.3 Oersted. In another embodiment, the annealedand un-annealed magnetic material may comprise substantially the samepercentage of rhenium, cobalt and phosphorus. In another embodiment, theannealed and un-annealed magnetic material may additionally comprise aportion of iron, according to the particular application. In anotherembodiment, the magnetic material may additionally comprise iron.

Benefits of the present invention include the enabling of high-frequencyinductors and transformers with magnetic films that are capable ofoperating at frequencies above about 30 MHz. Secondly, the use of twolayers of magnetic material leads to a significant increase ininductance, so that magnetic vias are needed. Third, it is difficult todeposit thicker films (5˜10 microns) using conventional sputtertechniques, so the electroplating methods described herein areadvantageous for the formation of thicker films. Fourth, the resistivityof the new alloys presented herein are substantially higher (˜150 μΩ-cm)than that of other materials such as NiFe (˜16 μΩ-cm) and CoZrTa, whichwill result in less eddy current dampening at high frequencies. Fifth,the new alloys of CoPRe, CoPReFe can sustain their excellent magneticproperties up to temperatures of about 330 degrees Celsius.

Although the foregoing description has specified certain steps andmaterials that may be used in the method of the present invention, thoseskilled in the art will appreciate that many modifications andsubstitutions may be made. Accordingly, it is intended that all suchmodifications, alterations, substitutions and additions be considered tofall within the spirit and scope of the invention as defined by theappended claims. In addition, it is appreciated that certain aspects ofmicroelectronic devices, such as microelectronic structures, are wellknown in the art. Therefore, it is appreciated that the Figures providedherein illustrate only portions of an exemplary microelectronic devicethat pertains to the practice of the present invention. Thus the presentinvention is not limited to the structures described herein.

1. A method comprising: forming a magnetic material on a substrate,wherein the magnetic material comprises rhenium, cobalt and phosphorus;and annealing the magnetic material at a temperature below about 330degrees Celsius, wherein the coercivity of the annealed magneticmaterial is below about 1 Oersted.
 2. The method of claim 1 whereinforming the magnetic material further comprises wherein the coercivityof the magnetic material is decreased by the addition of the rhenium. 3.The method of claim 1 further comprising wherein the magnetic materialis formed by using an electroplating process, wherein an electroplatingbath of the electroplating process comprises a cobalt salt, a rheniumsalt and a phosphorous source.
 4. The method of claim 1 furthercomprising wherein the magnetic material is formed by one of DCelectroplating, pulse reverse electroplating and pulse plating.
 5. Themethod of claim 1 wherein the magnetic material is formed by forming afirst nanolayer of magnetic material and then forming a second nanolayerof material on the first nanolayer of magnetic material.
 6. The methodof claim 5 wherein one of the first nanolayer and the second nanolayercomprises a percentage of phosphorus that is greater than the other ofthe first nanolayer and the second nanolayer.
 7. The method of claim 1wherein forming the magnetic material further comprises alternatingnanolayers of high phosphorus percentage material which may be magneticor non-magnetic with low phosphorous percentage magnetic material toform a multinanolayer magnetic material.
 8. The method of claim 1further comprising wherein the magnetic material comprises a rheniumpercentage of about 0.1 to about 5 atomic percent.
 9. The method ofclaim 1 further comprising wherein the magnetic material comprises iron,and wherein a magnetic flux saturation of the magnetic materialcomprises about 2.0 Tesla and below.
 10. A method comprising: forming amagnetic material comprising rhenium, phosphorus and cobalt on asubstrate, wherein the magnetic material comprises a portion of aninductor structure, and wherein the magnetic material comprises acoercivity below about 1 Oersted; and annealing the magnetic material ata temperature below about 330 degrees Celsius, wherein the coercivity ofthe annealed magnetic material remains below about 1 Oersted.
 11. Themethod of claim 10 further comprising wherein a permeability of themagnetic material comprises about 600 to about 800 from about 0 to about150 MHz.
 12. The method of claim 10 further comprising wherein aresistivity of the magnetic material comprises between about 100 microohm-centimeters to about 200 micro-ohm centimeters.
 13. A structurecomprising: a magnetic material comprising rhenium, phosphorus andcobalt on a substrate, wherein the atomic percentage of phosphoruscomprises about 8 to about 25 percent and the atomic percentage ofrhenium comprises about 0.1 to about 5 percent, and wherein the magneticmaterial comprises a coercivity below about 1 Oersted; and wherein themagnetic material comprises a portion of an inductor structure.
 14. Thestructure of claim 13 wherein the magnetic material comprises a seriesof alternating nanolayers of a high phosphorus percentage nanolayer anda low phosphorus percentage nanolayer.
 15. The structure of claim 14wherein the high phosphorus percentage nanolayer comprises a thicknessof below about 5 nm and the low percentage phosphorous nanolayercomprises a thickness of about 40 nm or less.
 16. The structure of claim13 wherein the magnetic material comprises a thickness of about 0.5microns to about 30 microns.
 17. The structure of claim 13 wherein themagnetic material comprises iron, and wherein a magnetic flux saturationof the magnetic material comprises about below about 2.0 Tesla.
 18. Thestructure of claim 13 wherein a wherein a resistivity of the magneticmaterial comprises between about 100 micro ohm-centimeters to about 200micro-ohm centimeters, and wherein a permeability of the magneticmaterial comprises about 600 to about 800 from about 0 to about 150 MHz.19. The structure of claim 13 wherein the structure comprises a portionof package structure comprising a multilevel metallization CMOSstructure.
 20. The structure of claim 13 wherein the inductor structurecomprises a portion of at least one of an on-chip and an on-packagevoltage converter, an RF high-frequency circuit, an EMI noise reductioncircuit and radar circuitry.